Image forming apparatus having developer replenishment control

Abstract

An image forming apparatus includes an image bearing member and a developer replenishment device. In addition, a control portion executes a first mode of detecting a first toner image for control by a sensor and controlling an operation of the replenishment device so that a detection result from the sensor attains a first target value, a second mode of detecting a second toner image for control by the sensor and setting a development contrast of a maximum image density so that a detection result attains a second target value, and a third mode of detecting a third toner image for control by the sensor and changing, based on the detection result, at least one of the first target value and a development contrast of the first toner image for control, wherein the control portion executes the third mode according to a timing at which the second mode is executed.

What is claimed is: 
     
       1. An image forming apparatus, comprising:
 an image bearing member; 
 an electrostatic image forming device which forms an electrostatic image on the image bearing member; 
 a developing device which develops the electrostatic image on the image bearing member by causing a developer including toner to be carried on a developer carrying member; 
 a replenishment device which replenishes the developing device with the developer; 
 a sensor which detects a toner image and which outputs information corresponding to a toner borne-on quantity; and 
 a control portion controlling an operation of the replenishment device based on a detection result of a first image having an intermediate density level detected by the sensor and a target value, and controlling a development contrast of a maximum image density based on a detection result of a second image detected by the sensor, 
 wherein the control portion controls the target value or the development contrast of the first image based on a detection result of a third image detected by the sensor, and 
 wherein the third image is formed in response to the timing of forming the second image. 
 
     
     
       2. An image forming apparatus according to  claim 1 , wherein the control portion forms the third image after forming the second image and before executing a subsequent image forming operation. 
     
     
       3. An image forming apparatus according to  claim 1 , wherein a development contrast of the third image is the same as a development contrast of the first image, and the control portion sets the target value based on a detection result of the third image detected by the sensor.